There are known methods and apparatuses for measuring electric potentials of biosignals in plants and animals (including humans), low-frequency signals on the ground or similar environmental objects, and other signals of various subjects. Another known technique permits an information processing terminal such as a personal computer (PC) to collect electric potential measurement data from those measurement apparatuses via wired or wireless communication links.
For example, there is a known technique to provide electrodes on clothes a person who is a test subject wears, and to detect biological signals of the test subject by using the electrodes; and another known technique to externally send and collect signals detected by a medical device implanted in a human body. Moreover, there is another known technique to paste, for example, three external electrodes (a positive electrode, a negative electrode, and an indifferent electrode), which are coupled to the main body of an electrocardiograph via wiring (leads), to a test subject's body surface and measure an electrocardiogram. Still another known technique is to measure an electrocardiographic waveform of a test subject in a measurement posture in contact with three exposed electrodes (a positive electrode, a negative electrode, and an indifferent electrode) which are provided at specified positions on a surface of an electrocardiograph.
The electric potential measurement using electric potential measurement apparatuses like those described above is performed by detecting signals at a plurality of measurement points on the subject. An electric potential observed at one of those points is used as a reference electric potential for measurement of signals at other points.
Japanese Laid-open Patent Publication No. 2010-22623 Japanese Patent No. 2655204
Japanese Laid-open Patent Publication No. 2009-118999
Japanese Laid-open Patent Publication No. 2010-12161
A type of electric potential measuring apparatus, whose electrodes for detecting signals at respective measurement points, including a measurement point for the reference electric potential, are coupled to the main body of the apparatus via wiring in order to measure electric potentials at a plurality of measurement points, has a problem of requiring burdensome work to connect wires. The wiring between the electrodes and the main body of the apparatus may be eliminated with respect to the measurement points, except the measurement point for the reference electric potential, for example, by wirelessly transmitting measurement data. However, if the wiring between the electrode for detecting a reference signal to obtain the reference electric potential and the main body of the apparatus is eliminated, the signal may be disturbed and the reference electric potential may fluctuate, and accordingly the electric potential may not be properly measured.
Another known apparatus is a portable-type electric potential measuring apparatus in which a plurality of exposed electrodes, including an electrode for detecting a reference signal, is provided on a surface of the main body of the apparatus, and which detects signals without using wiring between measurement points and the main body of the apparatus. The above-mentioned problem of requiring burdensome work for connecting wires does not occur in the case of such a portable-type electric potential measuring apparatus. However, with such an electric potential measuring apparatus, the electrode for detecting the reference signal, among the plurality of electrodes exposed on the main body of the apparatus, is located at a position distant from other signal detecting electrodes along a signal propagation path in the measurement subject. As a result, the arrangement of the electrodes on the main body of the apparatus is mostly fixed in a certain pattern, thereby possibly causing problems such as, for example, shape limitations in measurement subjects which may be measured, positional limitations in the measurement points on the relevant measurement subject, and limited type(s) of measurement subjects which may be measured.
The conventional electric potential measuring apparatuses as described above use one of signals, which are similarly detected at the plurality of measurement points, as the reference signal and use other signals as target signals whose electric potential is to be measured. When the electrodes, which are placed at the plurality of measurement points, and the main body of the relevant apparatus are connected via wiring in such an electric potential measuring apparatus, electric potentials of the measurement subject may not be sometimes easily measured. Moreover, in the case of an electric potential measuring apparatus which does not require wiring, the reference electric potential may be disturbed and the electric potential of the target signal whose electric potential is to be measured may not be measured properly. Furthermore, the electrode for detecting the reference signal is located at a position distant from the electrodes for detecting the signals whose electric potential is to be measured, along the signal propagation path in the measurement subject. So, targets on which the electric potential measuring apparatus is to be used may be limited.